title: Near-infrared fluorescence imaging of liver metastases in rats using indocyanine green.
abstract: BACKGROUND
  Near-infrared (NIR) fluorescence imaging using indocyanine green (ICG) is a promising technique to obtain real-time assessment of the extent and number of colorectal liver metastases during surgery. The current study aims to optimize dosage and timing of ICG administration.
  
  
  METHODS
  Liver tumors were induced in 18 male WAG/Rij rats by subcapsular inoculation of CC531 rat colorectal cancer cells into three distinct liver lobes. Rats were divided in two groups: imaging after 24 and 48 h or 72 and 96 h after intravenous ICG administration. In each time group, rats were allocated to three dose groups: 0.04, 0.08, or 0.16 mg ICG. Intraoperative imaging and ex vivo measurements were performed using the Mini-FLARE imaging system and confirmed by fluorescence microscopy. Fluorescence intensity was quantified using the Mini-FLARE software and the difference between tumor signal and liver signal (tumor-to-liver ratio; TLR) was calculated.
  
  
  RESULTS
  In all 18 rats, all colorectal liver metastases (n = 34), some as small as 1.2 mm, were identified using ICG and the Mini-FLARE imaging system. Average tumor-to-liver ratio (TLR) over all groups was 3.0 ± 1.2. TLR was significantly higher in the 72 h time group compared with other time points. ICG dose did not significantly influence TLR, but a trend was found favoring the 0.08 mg dose group. Fluorescence microscopy demonstrated a clear fluorescent rim around the tumor.
  
  
  CONCLUSIONS
  This study demonstrates that colorectal cancer liver metastases can be clearly identified during surgery using ICG and the Mini-FLARE imaging system, with optimal timing of 72 h post-injection and an optimal dose of 0.08 mg (0.25 mg/kg) ICG. NIR fluorescence imaging has the potential to improve intraoperative detection of micrometastases and, thus, the completeness of resection.
authors.affiliation: Department of Surgery, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Joost R
authors.initials: JR
authors.lastname: van der Vorst
authors.forename: Merlijn
authors.initials: M
authors.lastname: Hutteman
authors.forename: J Sven D
authors.initials: JS
authors.lastname: Mieog
authors.forename: Karien E
authors.initials: KE
authors.lastname: de Rooij
authors.forename: Eric L
authors.initials: EL
authors.lastname: Kaijzel
authors.forename: Clemens W G M
authors.initials: CW
authors.lastname: Löwik
authors.forename: Hein
authors.initials: H
authors.lastname: Putter
authors.forename: Peter J K
authors.initials: PJ
authors.lastname: Kuppen
authors.forename: John V
authors.initials: JV
authors.lastname: Frangioni
authors.forename: Cornelis J H
authors.initials: CJ
authors.lastname: van de Velde
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Vahrmeijer
mesh_terms: D000818:Animals; D002277:Carcinoma / Q000175:diagnosis* / Q000556:secondary; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000473:pathology*; D004396:Coloring Agents / Q000008:administration & dosage; D003952:Diagnostic Imaging / Q000379:methods; D007208:Indocyanine Green / Q000008:administration & dosage; D007432:Intraoperative Period; D008114:Liver Neoplasms, Experimental / Q000175:diagnosis* / Q000556:secondary; D008297:Male; D051381:Rats
chemical_list: D004396:Coloring Agents; D007208:Indocyanine Green